Resource Recovery from Food Processing Wastes

The wastes from food industry, after recovery and further processing, can be used for different purposes: the recovered materials can either be recycled, or be used to recover energy by incineration or anaerobic digestion. Recycling not only reduces the environmental impact of the material, but also helps to satisfy the increasing demands for raw materials. In addition, it also reduces disposal costs, a key driver of recycling technologies. For instance, fruit, vegetables and meat processors generate large quantities of solid wastes. Table 1 lists examples of useful materials which can be recovered from fruit and vegetable wastes.

Recovered materials can be used in various ways. Solid food wastes can be used as animal feed after reducing their water content. A good example of this practice is soybean meal, a byproduct of soybean oil extraction, which was simply discarded previously but is now used as animal feed on account of its high nutritive value. Solid wastes can also be upgraded by fermentation. A number of fermented foods are produced this way. Composting and ensilaging are also examples of solid waste fermentation process. Solid wastes rich in carbohydrate can also be converted to sugars by enzyme-assisted hydrolysis: an example is the enzymatic hydrolysis of lactose and galactose sugar using galactosidase. Solid wastes rich in sugar can be fermented to produce carbon dioxide and ethanol. The latter a valuable product, and has also been earmarked as an alternative fuel for the future.

As mentioned above, solid wastes can also be utilized as fuel directly or converted to methane by anaerobic digestion in a bioreactor. Biological hydrogen is produced by fermentation of both glucose and sucrose in food processing wastes under slightly acidic conditions in the absence of oxygen. This can be achieved by using a variety of bacteria through the actions of well studied anaerobic metabolic pathways and hydrogenase enzymes. Hydrogen has 2.4 times the energy content of methane, i.e. on a mass basis; and its reaction with oxygen in fuel cells produces only water, a harmless byproduct. Hydrogen gas has valuable potential for producing clean and economical energy in the near future.

Table 1 Some examples of products which can be recovered or made from fruit and vegetable wastes.